This invention is a plug washer that is useful for connecting steel support members to masonry walls, such as walls made of concrete, brick, cement block, stone or the like, all hereinafter referred to as masonry. Although masonry walls have great ability to resist compressive loads, they are not good at resisting horizontal stresses. Masonry walls are particularly vulnerable in regions subject to earthquakes. Older structures in earthquake-prone regions or structures damaged by earthquakes should be retrofitted to resist earthquakes or provided with a steel support structure when being repaired after being damaged in an earthquake.
To retrofit structures for earthquake resistance it is common to build a supporting steel framework adjacent to the masonry walls to prevent horizontal stresses from toppling the walls. The supporting steel framework is usually built inside the structure and the supporting steel must be firmly connected to the masonry walls to hold the support structure and the masonry walls together. This is usually accomplished by drilling holes in the masonry and in the support steel, embedding studs in the holes in the masonry so that they extend through corresponding holes in the steel support framework and then connecting the framework to the wall with nuts, or the like, to hold the steel framework in supporting relationship with the masonry. It has been determined that a stud embedded in masonry at an angle oblique to horizontal will have greater strength than one embedded to extend horizontally, from the masonry wall. It has further been determined that a stud embedded at an angle of 22.5 degrees from horizontal provides the strongest connection.
There are many ways to embed studs in masonry including expansion elements of various types placed in holes in the masonry and then expanded by the torque of a bolt screwed into the expansion element. A very suitable way to embed a stud in a masonry wall is to put epoxy cement in a hole in the wall and to insert a stud in the hole so that the epoxy surrounds it. The amount of epoxy placed in the hole is such that when it is displaced by insertion of the stud it will just fill the hole. The bond between epoxy and masonry is stronger than the masonry itself and the bond is also stronger than the stud. An epoxy resin can be made viscous enough to flow from such a hole very slowly.
One problem with such a system is that it is difficult to have pre-drilled holes in masonry and pre-drilled or punched holes in steel support members correspond when they are placed together. A drill bit characteristically "walks" from the desired center of the hole when drilling starts so that the centers of the holes in masonry and the holes in the steel support member do not exactly correspond. In such cases the studs extending from the masonry wall cannot pass through the holes in the steel support member that were drilled or punched to receive them. When the studs extending from a masonry wall do not correspond in position with the pre-prepared holes in a steel support member costly and time-consuming revision of the holes or the studs must be made to provide adequate support. Another problem is that a nut screwed onto a stud that is at an oblique angle from horizontal cannot make a flat bearing against a vertical steel support element. Tightening a nut that is at an angle to its proposed bearing surface will provide unreliable holding force and it will tend to cause the stud to bend which reduces the ultimate strength of the stud.
Although washers are known that accommodate to surfaces that are at an oblique angle to a stud, those washers have a central hole that is much larger than the diameter of the stud that is to be received in that hole because the central hole must accommodate the stud passing through it at an angle oblique to horizontal. Even if a washer lies flat against the support member, the nut on such a stud cannot bear flatly against the washer because of the angle of the stud. The bearing force of a nut accordingly is not uniformly distributed on the washers so that the holding force of the nut is diminished. Additionally, in studs that are held with epoxy or other liquid-phase or plastic cement, some of the cement may flow out of the hole in the masonry thereby diminishing the strength of the bond.